Cellular Activities Movements through Membranes

Structure Phospholipid bilayer Proteins Glycoproteins Cholesterol

Function of cell membrane How selective permeability is created:  Molecules that are watery How do they get in? If they are small If they are large  Molecules that are large  Molecules that dissolve in fats

Background Structure of cell membrane – phospholipid bilayer  Is a fat  The third fatty acid is replaced with an inorganic phosphate The molecule is amphiphilic

Cell Movements Diffusion – passive transport  Definition

Diffusion Gradient Equilibrium Examples of molecules Animation 

Osmosis - passive Definition Terms  Hypertonic – has a high solute concentration or low water concentration  Hypotonic - has a low solute concentration or high water concentration  New definition of osmosis: movement from a hypotonic solution to a hypertonic solution  Isotonic – equal water concentration

Osmosis Animation hill.com/sites/ /student_view0/chapter2/animation__how_osmosis_works. html hill.com/sites/ /student_view0/chapter2/animation__how_osmosis_works. html

Examples of Osmosis Osmotic Pressure – the pressure required to stop the osmotic flow of water  Water moves into a hypertonic solution but what if too much water was entering and needed to be stopped.  Occurs in plants

Examples – see page 187 Isotonic cells are placed in isotonic solutions:  Cells neither gain or lose water

Cells are placed in hypotonic solutions Animal cells will swell & burst Plant cells swell and place pressure against the cell wall  Why is this good in a plant cell?

Cells are placed in hypertonic solutions Animal cells shrink – creanate ( they undergo plasmolysis, loss of water by a cell) Plant cells – the vacuole collapses

Facilitated Diffusion - passive Definition – use of transport proteins to move materials across a membrane Why must it occur – some materials are hydrophilic and can not get through the bilayer How does it work – a channel is created by the protein so the watery materials do not contact that part of the bilayer

Example of Facilitated Diffusion It is passive because the movement is down a gradient.

Active Transport Definition – movement of materials against a gradient.

Pumps The membrane protein moves the material across the membrane either by binding to the material to b transported or by physically changing the shape of the channel to fit the material needed to be moved. Example – sodium-potassium pump

Movements of the Membrane Endocytosis – the cell engulfs the particle and moves the particle inside  Types: Phagocytosis Pinocytosis

Movements of Membrane Exocytosis – a vesicle forms around a large solid particle and it is removed from the cell.

Metabolism Definition – all the reactions that occur in the cell  Include making and breaking large molecules

Types of Metabolic Reactions Hydrolysis/Catabolism  Breaking large molecules into smaller molecules by adding water  EXAMPLE: Breaking a disaccharide into two monosaccharides: sucrose + water -> glucose + fructose  BEST EXAMPLE: cellular respiration – breaking glucose to release energy.

Types of Metabolic Reactions Condensation/Dehydration Synthesis/Catabolism  Joining small molecules to form large molecules by removing water  EXAMPLE: Building a disaccharide from two monosaccharides: glucose + fructose -> sucrose + water  BEST EXAMPLE: photosynthesis – producing glucose by using the sun’s energy

Homeostasis Definition – maintaining a steady internal environment  How is it maintained – by letting materials pass in and out of the cell.

Enzyme Reactions – chapter two Enzymes  Provide activation energy in living things  Activation energy – energy necessary to start a reaction. How enzymes provide activation energy: Increase the number of collisions between atoms and molecules; therefore bonds can be broken and new bonds formed.  Composition – proteins (tertiary or quartenary)

Structure of enzyme Have active sites

Enzyme Action Lock and key hypothesis  Shows enzymes have active sites  Shows enzymes are reusable  See p. 52

Enzyme Regulations Necessity  Enzyme regulation by pepsin Illustrates need for regulation  Types: pH – optimal pH Temperature – enzymes have an optimal temperature One at which the shape will not be destroyed but the greatest number of collisions occur Denaturing an enzyme pH – optimal pH

Enzyme Regulations Competitive inhibition – another molecule is shaped like the substrate and competes for the enzyme Feedback inhibition – an accumulation of products inactivates the first enzyme in a series Precursor activation - the presence of the first substrate activates all enzymes in the series. Animation of enzyme action - /Biology1111/animations/enzyme.html /Biology1111/animations/enzyme.html